Question: 9 crayons cost $10.71. Which equation would help determine the cost of 5 crayons?
Explanation: There are several equations that could help determine the cost, each with a slightly different approach. We know the cost of 9 crayons. We want to know the cost of 5 crayons. We can write the numbers of crayons as a proportion: $\dfrac{9}{5}$ We know 9 crayons costs $10.71. We can let $x$ represent the unknown cost of 5 crayons. The proportion of these costs can be expressed as: $\dfrac{\$10.71}{x}$ The cost changes along with the number of crayons purchased, and so the two proportions are equivalent. $\dfrac{9}{5} = \dfrac{\$10.71}{x}$